As a guy who likes to run solo with a reaper emissary flag. Usually the most successful encounters are those that start with surprise and the enemy ship is parked. I usually sail up at an angle behind them where their cannons cant get me but I have sight on their stern and side hull. I raise my sails, take out the mast first with chain shot, then lay into them with cannon fire. After a good bit of that I usually set my ship to moving slowly to deter boarders and go board them to hold then off till they sink.
When I dont have the element of surprise it is usually a fight of attrition and has a high chance to end badly. All it takes is getting hit in the face with a cannon ball at a bad time against an experienced crew and you are done. Sometimes I am able to end these attrition fights early by hitting their sails ,putting some holes in them, and boarding. Usually this only works against sloops or very inexperienced brig/galleon crews as it requires solo killing the entire crew.
In these kinda of fights I recommend getting a feel for your opponent. If they aren't on a sloop, can properly maneuver their ship ,and their cannoners aren't drunk on grog, it is usually time to peace out. If they are on a sloop, well, hope their cqc skills arent as good as their aim and have at it.
I have also had great success parking my ship behind a near by island and rowboating in. Lots of players dont check the map for reapers often enough. The goal here is usually to light up their ship with firebombs and ram it into things till it sinks.
Other tips include: Always bring food better than coconuts.
Have your regen bar full before you start a fight.
Dont bring wood or cannonballs to a boarding action. You want to steal there's and eat their food if you can.
I have found as a solo, gunpowder kegs in the crowd nest are a liability. Lose your mast while you are solo and more often than not you are dead. If you store them somewhere else they will fill the ship full of holes. Best alternate location is behind the map table. You will get pretty hurt if you are on the wheel if one detonates but the ship will at least keep moving.